This disclosure relates to the field of agricultural implements and in particular such implements with increased flotation and resistance to sinking into soft soil.
A common problem that farmers can experience at seeding time is the inability to seed their crops because excessive soil moisture makes the fields unable to support the seeding equipment, typically due to excessive or untimely rainfall. Sometimes as well heavy snow cover produces a lot of moisture which must either run off the fields, be absorbed by the soil or evaporate. A late, cool spring can slow the soil drying process considerably. Unfortunately, for maximizing crop yields and crop quality and also minimizing the chances of crop damage or complete crop losses for spring seeded crops, it is necessary for farmers to seed their crops within the finite window of time indicated as acceptable by past experience.
Seeding too late, especially in northern agricultural areas, exposes the crop to the risk of frost before the crop matures. This risk is recognized in some crop insurance regimes where crops must be seeded before a specified date in order to qualify for crop insurance. As farm sizes, crop input costs, land costs, and the like increase, the negative consequences for failing to seed a crop increase as well.
Agricultural air seeders are typically used to place seed and fertilizer in the soil to plant a crop. Such air seeders typically include a frame mounted on wheels for movement along the ground, and furrow openers mounted to the frame and spaced evenly across the width of the frame so that furrows and thus seed rows are evenly spaced across the field. The frame includes a hitch extending forward from the front end thereof and the drawbar of a towing tractor is attached to the front end of the hitch by a pin, such that the frame is pivotally attached to the drawbar about a vertical pivot axis provided by the pin.
To provide even emergence of the crop plants, and to maximize yields, it is desirable to place the seeds at a consistent depth beneath the soil surface. One common design to accomplish this is to provide front and rear wheels along corresponding front and rear edges of the frame, so that the front and rear edges are then at a distance above the ground that is substantially the same regardless of ups and downs in the field terrain and is thus kept level. The furrow openers are located between the front and rear wheels.
In air seeders with furrow openers mounted directly to the drill frame, the furrow openers extend the same distance downward from the frame so that the depth to which each furrow opener penetrates the soil is substantially the same, and is controlled by moving the front and rear wheels up and down with respect to the frame.
In air seeders with independent ground following openers, each furrow opener is independently mounted on an arm with a ground following wheel, and a hydraulic cylinder exerts a downward bias force between the frame and the arm that pushes the furrow opener into the soil, and forces the ground following wheel against the soil behind the furrow opener to pack the soil over the seed. The relative position of the furrow opener and ground following wheel is adjusted to substantially control the penetration depth. The hydraulic cylinders also raise the arms to transport and lower them for field work.
Such independent furrow openers have been found to perform better in soft, wet soil conditions than the frame mounted openers, as the ground following wheel prevents the furrow opener from sinking further into the soil if the frame wheels sink in the soft soil. Seeding depth is thus better controlled, and the downward bias force exerted on the arm can be reduced where the soil is very soft. The weight of the implement is also partially carried on the ground following wheels, thus somewhat reducing the weight on the front and rear frame wheels, and reducing the tendency for the front and rear fame wheels to sink into soft soil.
The rear wheels are typically fixed to the frame such that the rotational axes thereof are perpendicular to the operating travel direction. Typically as well, the front wheels are caster wheels that can pivot freely about a vertical caster axis. The fixed rear wheels keep the implement moving in a straight line following the tractor, while the castering front wheels allow the implement to turn since the rolling orientation of the caster wheels changes to follow the frame as it moves in a lateral direction during the turn.
A “floating” type hitch is pivotally attached to the frame about a hitch pivot axis oriented horizontally and perpendicular to the operating travel direction. The front end of the hitch connects to the tractor drawbar, and the floating hitch pivots up and down with the tractor drawbar and the frame as the tractor and implement move across a field and as terrain varies. This same arrangement is used on agricultural implements such as cultivators and the like, in addition to air seeders. The frame of a modern agricultural implement can be 80 feet or more wide, and so the frame is divided into side by side wing sections that pivot with respect to each other about frame pivot axes oriented parallel to the operating travel direction.
The front and rear frame wheels must support the weight of the implements, and in addition, ground engaging tools are often configured to draw them selves into the ground, thereby exerting additional downward forces that must be carried by the wheels. Compounding this problem is the fact that on floating hitch implements, the tractor drawbar is often lower than the hitch pivot axis, which results in an additional downward force component on the front of the frame, especially on the center section where the hitch is attached. Thus in soft soil conditions, the wheels, and the front wheels in particular, sink into the soil such that rolling resistance and draft forces increase significantly. Especially with frame mounted opener air seeders and cultivators without independent ground engaging tools, the depth of penetration of the ground engaging tools increases, which undesirably increases seed depth placement in an air seeder, and also further increases draft in all implements. When the soil is very soft as in wet weather, the implement can become stuck, and it is not then possible to carry on the seeding operation.
Significant problems with wet conditions at seeding time were encountered for example in large areas of western Canada during the spring of both 2010 and 2011, with many fields going unseeded because the window of suitable time closed before the fields were dry enough for the farmers to operate their seeding equipment.
Considerable advice was circulated with respect to working wet fields with air seeders, such as reducing down pressure on furrow openers, changing packer wheels, altering travel paths, and the like. It was generally accepted that air seeders with independent ground following openers worked better, but in many areas the soil was too wet for these air seeders. Many farmers seeded by simply broadcasting seed on the soil, often from airplanes.
Significant effort was devoted to providing increased flotation for air seeders in an attempt to keep them operative in very wet field conditions. Some offered larger front caster wheel tires in an attempt to provide increased flotation, however it is not possible to significantly increase the diameter of the tires. Some farmers fitted track assemblies in place of the front caster wheels. Seed Master™ of Regina, Canada recommended an optional lift kit for their air seeders to reduce the problem of getting stuck. The lift kit reduced the weight on the front caster wheels by transferring weight from the front caster wheels to the tractor drawbar and to the rear wheels through an arrangement described in Canadian Patent Application Number 2,645,522.
Increasing the diameter of a wheel generally provides a greater improvement in flotation and reduced rolling resistance compared to increasing the wheel width, and so it is desirable to provide larger diameter wheels. The diameter of the fixed rear wheels may be increased significantly to provide an increased support area of contact with the ground, however increasing the diameter of the castering front wheels that are pivotally attached to the frame through caster pivots is problematic for a number of reasons.
The hitch to tow the implement is attached to the center section, and the front wheels supporting the center section must be mounted on either side of the hitch. In order to use a large diameter castering flotation tire on the front of this center section the castering wheels would need to be moved away from the hitch such that there is sufficient distance on each side to provide a clear pivot envelope for the large diameter wheel to pivot between the caster axis and the hitch as it pivots through 360 degrees. In some implements it is known to support the front of the center section with a single caster wheel assembly in the middle of the center section, instead of mounting one on each side, however with larger implements with wing sections extending from each side of the center section, this arrangement lacks stability, especially when in transport.
If the size of the front caster wheel is increased significantly, such as to twice the diameter for example, the caster bracket will need to be significantly larger, stronger, and more costly. The distance between the caster axis and the wheel/ground contact surface increases proportionally, and the 360 degree envelope becomes problematic. Moving these center section front caster wheels wide enough apart to provide this clear envelope results in an excessive distance between the wheels, such that travel on roads during transport is difficult, if not impossible. The wider spacing also adversely affects ground contour following characteristics of the implement.
Such agricultural implements typically make a sharp turn at the end of a field pass, and the caster wheels twist against the ground as the caster axis moves sharply with the implement frame causing soil disturbance. The twisting of a larger tire against the ground surface will exert increased forces on the caster bracket, and also create a larger soil disturbance. Such soil disturbance is particularly undesirable in modern no-till farming practices because conventional tillage is not carried out on the field surface, and so any ruts and disturbance made by an implement are not smoothed out by normal cultivation.
Thus increasing the diameter of the front wheels of agricultural implements would be highly beneficial by providing increased flotation, however the diameter is constrained by the need to allow the front caster wheels to pivot to vary the rolling orientation thereof and allow the front end of the implement to move laterally during turns.